Abstract

Solar wind
proton and alpha spectra from the Faraday Cup portion of the SWE experiment on the Wind spacecraft have been analyzed to determine the temperature anisotropy of each species, under the assumption of convected, bi‐Maxwellian distributions. From the start of the mission in late 1994 to date we have collected over 2 million measurements of the anisotropies in the solar wind. This dataset is sufficiently large to conduct a statistical study, comparing the observed temperature anisotropies to various limits imposed by instabilities. Specifically we will discuss the effects of the firehose, mirror, and cyclotron instabilities. With a limit to the proton temperature anisotropy established, we examine several cases where this limit is approached or exceeded and comment on magnetic field activity and alpha parameters during these intervals. In the large plasma beta regime we illustrate evidence of a transition from the cyclotron to the mirror instability as the dominant limit.